1. Field of the Invention
The present invention relates to a high density magnetic recording system having magnetic heads adapted to provide a high data transfer rate (higher than 15 Mbyte/sec) with a high linear speed (&gt;27.9 m/sec=&gt;1100 inches per second) and high recording density with low spacing loss and excellent signal quality from the start to the end of a scan. Such a system might involve either longitudinal or helical tape recording that uses a ring head.
2. Description of the Prior Art
As data transfer rate and recording density increase in magnetic recording, head spacing loss becomes more critical. Magnetic head spacing loss is dependent upon many variables, including radius of curvature of the head and is also dependent upon how the tape contacts the head while the scanner rotates. When scanner speed increases, head-to-tape spacing also generally increases since air film thickness between the head and tape increases. In the usual helical scanner there are two record heads and two playback heads. Each head has two tips. Therefore, eight rotating tips individually contact (or come into magnetic relationship with) the tape. Ideally, each tip should maintain a minimum spacing with respect to the tape while the scanner rotates. If there is significant spacing variation while the scanner rotates, this will result in variation in the signal output from each channel.
Various head configurations have been used in the prior art in connection with high density helical and/or longitudinal recording on tape. The style most applicable to the present system would generally fall within a class of ring heads that includes a pair of generally opposed core pieces oriented upon on either side of a gap structure with a winding window opening below the gap structure. The opposed core pieces are bonded together to form the magnetic head structure. The tape contact surface of the head is configured in a curved shape of relatively large radius in the direction parallel to the direction of tape travel. The width of the head is usually uniform from the leading edge to trailing edge, and tape contact surface profile in the direction perpendicular to the direction of tape travel is generally of flat or mildly arcuate outline.
A variety of mechanisms have been used to minimize air pressure with respect to such heads, including the formation of slots in the head surface, parallel or perpendicular to the direction of tape travel. It has also been generally recognized that head wear, head contour, lifetime, tip projection, and performance factors such as tape head separation are all inter-related. Generally, heads that wear faster have less spacing between head and tape.
Previous investigators have observed that air film thickness at the leading edge of the head is generally greater than that at the trailing edge. Large air film thickness at the leading or trailing edge of the head may result in non-uniform signal output, either at the beginning or end of scanning. It is also well known that head-to-tape spacing generally increases with linear speed and decreases with tension.
One of the problems with high linear speed operation (&gt;27.9 m/sec) is to overcome spacing loss and to prevent bow-wave impact due to head-to-tape interaction with compressed air films at high speed and high tension It has been a big challenge to overcome high spacing loss and/or a high degree of head-to-tape interaction at high data transfer rate (&gt;15 Mbyte/sec). Even with extensive efforts to analyze tape flow, there are still many unknown aspects of the dynamics of head and tape in high speed helical recording.